A technology of charging a battery with power generated by utilizing natural energy and with power from a system is getting attention. As shown in FIG. 5, a battery control system realized by such a technology includes battery modules 1 that have a controller 6 controlling a battery 7 and are connected in series or in parallel as a group and a single relay 2 that comprehensively controls this group of the battery modules 1. Moreover, a battery system control device 3 that manages the respective battery modules 1 as a whole through a group of a plurality of the relays 2 is provided and thus a large-capacity battery 7 is realized. As described above, in a battery control system 8 disposing control devices as a hierarchical structure, the battery system control device 3 transmits a control signal for instructing charging, discharging or the like of the battery 7 to each battery module 1 through the relay 2 and manages the status of communication lines 4 and 5 for transmitting and receiving the control signal and the operation status of the control device itself (refer to PTL 1).